Color photography



Patented Jan. 16, 19:45

COLOR PHOTOGRAPHY Harry Edward Coote, North Wernbley, England ,No Drawing. Application January 8, 1943, Serial No. 471,697. In Great Britain January 18, 1942 2 Claims.

7 This invention relates to color photography and is concerned with methods 'of obtaining independent color separation records from two or more differently color-sensitized emulsion layers inseparably superposed on one side of a single transparent support after the emulsion layers have been simultaneously exposed to light.

In one known method of color photography two color-sensitized emulsion layers are carried on one support and a third color-sensitized layer is carried on a second support while in another I method all three color-sensitized emulsion layers are superposed on one and the same support. In the first case, an independent color-separation record can be obtained by ordinary photographic methods from the single emulsion layer on the one support, but to obtain independent color separation records from the support carrying two or more superposed emulsion layers, these must be processed in various ways. One method of obtaining independent color-separation records has involved printing the images on both the emulsion layers onto separate plates by reflection printing and another method has involved the printing. of an intermediate singlelayered record of the inseparably superposed iniages.

Now the object oi-the present invention is to provide improved methods of obtaining independent color separation records from two or more inseparably superposed color-sensitized emulsion layers carried by a single support. The methods of the invention have the advantage that the necessity for the preparation of an intermediate single-layered print of the superposed images is obviated, while, when there are two superposed emulsion layers, only the image next to the support, which is quantitatively and qualitatively the best, is photographed by reflected light, or when there are more than two superposed layers, only the inner layers are photographed by reflected light.

According to the invention, in the case where there are two superimposed layers, the method comprises essentially the steps of developing the emulsion layers after exposure, bleaching the images in both layers, redeveloping the outer layer In thecase when there are three superposed emulsion layers on one support the processing and duplicating steps are repeated, so that a duplicate is next obtained of the image on the intermediate emulsion layer and after the image has been eliminated the image on the layer most remote from the support can be duplicated or printed by transmitted light.

In either case there is obtained an independent color separation negative of the image on the emulsion layer next to the support and, if there are-more than two superposed emulsion layers, also of the images on the intermediate layer or layers, while the imageon the top layer remote from the support remains as a normal negative on the original support.

The invention may be carried into effect in various ways.

Thus, where there are only two superposed emulsion layers, both layers, after being developed and fixed, are bleached to a silver salt by treatment in a bleaching bath which may be of known composition, and the layer remote from the support is redeveloped, for example by a loaded developer, leaving the image next to the support bleached. The negative is then photographed onto a separate single-layer emulsion,

the bleached image being outwards and being placed against a black background, and the single-layer emulsion is developed and fixed in the usual way so as to give a duplicate negative of the bleached image. The bleached image in the layer next to the support is then fixed out, for instance with thiosulphate, leaving the image in the layer remote from the support as an independent color separation negative on the origi nal support.

In applying the above-described method to a support carrying three or more superposed emulsion layers, a similar procedure is adopted, that is to say all the images are bleached to silver salt whereupon all except the image on the layer next to the support are redeveloped leaving the image nearest the support bleached. This image is then photographed in the manner previously described to yield an independent singlelayer negative. The multi-layer negative is then fixed so as to eliminate the bleached image next to the support and the remaining layers are bleached again and all the layers except the next but one layer to the support are redeveloped under controlled conditions so as to leave the next but one image to the support as a silver salt. This image is then photographed onto a separate single-layer emulsion as before, and is then fined out after which the procedure is repeated until all the layers are duplicated with the exception of the top layer which remains on the original support as a normal negative.

In order that the invention may be easily understood and readily carried into effect, the following example of preferred methods in accordance with the invention are given.

Example This example illustrates the application 01' the invention to a bi-pack arrangement in which one of the supports carries two difierently colorsensitized emulsion layers, namely, a blue-sensitive layer next to the support and a red-sexist tive layer superposed thereon, and the other sup= port carries only a, green-sensitive layer. The

two supports are exposed simultaneously in the Potassium ferricyanide "ounces-.. ll Potassium bromide do F1, Water to make pints 1 After bleaching, the upper image, that is the oneremote from the support, is redeveloped by means of a loaded developer, a suitable composi tion for which is as follows:

Hydroquinone grains Sodium sulphlte clo lilil Sodium hydroxide "do"-.. fill Glycerin ..ounoes 1 Water to do to The negative is then placed in stop bath to prevent further development. This bath may have the following composition:

Sodium bisulpllite i cranis a Glacial acetic acid do 2 Water to; ounces it The negative, after being rinsed, is then placed on a black background with the bleached image outwards and is photographed onto a separate single-layer emulsion, which after being developed and fixed in the usual manner, forms the second color separation negative. The two-layer negative is then fixed out, for example with sodium thiosulphate, so that the bleached image which i nearest to the film is eliminated, while the image in the top emulsion layer being silver and not a, silver salt is not affected. This image in the top layer remote from the support is thus left in the form of a negative on the original sup- .port and forms the third color separation negative.

In applying the method described above to a support carrying three or more'color-sensitized emulsion layers superposed on a single support, a similar procedure is followed, that is to say, all the images are bleached to a silver salt, whereascmass I upon all the images except that next to the support are redeveloped under controlled conditions, for example with the same loaded developer as before. The bleached image next to the support negative or the bleached negative image is then photographed against a black background in the manner previously described to yield an independent single-layer negative of this image. The multi-layer negative is then fixed out so as to eliminate the bleached image next to the sup port and the remaining layers are bleached again and all the layers except the next but one layer to the support are redeveloped with a loaded developer so as to leave the next but one image to the support as a. silver salt. This image is the" hotographed onto a separate single-layer on as previously described, and the pro-= repeated until all the layers are dupliith, the exception of, the top layer remote be support which remains on the original t in the form of an independent color sop or ion negative.

ill thus be seen that in all cases an indepen mlor separation record is produced each. one or a plurality oi emulsion layers in p ly po ed on one side of a single support. These records may be printed by transmitted light and used for color photography prom esses Various modifications may be made withou departing from the invention. For example, ot' developers and bleaching baths than those s fled may be used, and the differently color-so. tlsed emulsion layers may be arranged on support or supports in different order from t given in the example,

What I claim is:

l. A method of obtaining independei: separation photographic records from ea two color-sensitized emulsion layers insepe superposed on one side of a single support, v comprises the steps or developing and emulsion layers after exposure, bleachin layers to a silver salt, redeveloping only the remote from the support, making a dupli.

the support by photographing this image aganist a black background placed against the redevel oped image on a single-layer emulsion ing out the bleached image so as to leave image in the layer remote from the support as an independent color separation record.

2. A method of obtaining independent color separation photographic records from three or more color-sensitized emulsion layers inseparably superposed on one side of a single support, which comprises-the steps of developing and fixing all the emulsion layers after exposure, bleaching all the emulsion layers to a silver salt, redeveloping all the emulsion layers except t e lay r next to the support, making a duplicate of the bleached image next to the support by photographing this image against a black background placed against the redeveloped image, fixing out the bleached image, and repeating the bleaching, redeveloping, photographing and fixing out steps until the images in all the layers have been duplicated with the exception of that on the layer most remote HARRY EDWARD COO'I'E. 

